Importing 3rd Party Function Library not Recognized

We need to import a 3rd party function library to extend the script functionality of System Platform.
After importing, this library is not recognized by System Platform.
One possibility is that the library does not support the old ".NET Framework", but supports only the new ".NET".

Maybe is something that might be in progress already.
Can you help us or help us find someone who can address this topic?
Thanks!!